Conventional practices used in the abandonment of a subsea hydrocarbon producing, injection or disposal wells include cutting and removing individual portions or components of the subsea well in separate pieces. This is illustrated in FIGS. 1A-1F. FIG. 1A illustrates a subsea well 4 connected to a topsides rig 2, which can be a floating drilling or intervention vessel, by way of a marine riser 28 also referred to simply as a riser 28. A subsea well 4 generally includes a structural casing or conductor 18o, a surface casing 18o-1 and multiple concentric casings 18 located downhole, below the wellhead assembly 8 on, at or near the seabed 1, as well as associated components including hangers and seal assemblies (not shown) and other well components. The subsea wellhead assembly 8 typically includes a low-pressure wellhead housing 8A attached to the structural conductor 18o which is the outermost of the casings 18, and a high-pressure wellhead housing 8B attached to the surface casing 18o-1 which is the next outermost of the casings 18, and a blowout preventer (BOP) stack 9. As shown in FIG. 1B, a drill pipe 7 having a conventional cutter 3, which may be equipped with a spear assembly 22, near the end of the drill pipe 7 is used to cut individual well casings 18. Current casing cutter technology is limited in terms of the depth, radius and thickness of cuts that are possible. Currently, with the exception of the two outermost casings (18o and 18o-1), no more than one well casing 18 can be cut at a time, which in some cases is due to cutting tool 3 dimensional limitations. Therefore each inner casing 18 must be individually cut and retrieved from the subsea well 4 to the floating drilling or intervention vessel 2 at the surface of the water 11. Multiple drill string trips or instances of running the drill pipe 7 and cutter 3 into and out of the well 4 are required to remove each of the individual well casings 18 and components separately as shown in FIGS. 1B-1F. The inner casing strings 18 are cut and retrieved separately. For one, cutting tool 3 dimensions, clearances and cutting arm lengths restrict the depth of cuts possible on inner casings 18. Additionally, the presence of casing hanger seals dictates that the seals be removed separately so that the innermost casing 18i can be cut and retrieved before cutting the next casing string 18i+1. As shown in FIG. 1C, after the innermost casing 18i is removed, cement can be delivered to the well to form a plug 34. This process is repeated for all of the inner casing strings 18 as shown in FIG. 1D. As shown in FIG. 1E, after all of the inner casing strings 18 have been cut and recovered and only the two outermost casings (18o and 18o-1) and the well head assembly 8 remain, the BOPs 9 and the riser 28 are recovered to the surface and stored on the rig 2. At this point, as shown in FIG. 1F, only the two outermost casings, the structural casing 18o and the surface casing 18o-1 remain. The large diameter inside the surface casing surface casing 18o-1 provides enough clearance dimensionally for longer blades to be used which can cut through both the structural casing 18o and the surface casing 18o-1 at one time. The two principal components of the wellhead assembly 8, the low pressure well head housing 8A and the high pressure wellhead housing 8B, are locked together at this point and must be recovered as a single unit. Cement is introduced into the well 4 following the removal of each casing 18 to form plugs 34. FIG. 1G illustrates the resultant abandoned well 4.
Conventional practices involving the multiple drill string trips required to remove each of the individual well casings 18 and components separately are time-consuming and costly. The multiple lowering and raising of the drill pipe 7 and cutter 3, and multiple trips with the spear assembly 22 also create greater potential for safety incidents, equipment downtime and weather delays.
An improved process for subsea well abandonment, subsea wellhead recovery and/or subsea well plugging that avoids the aforementioned problems would be desirable.